The invention relates to a tread for a pneumatic tire. The treated is particularly well suited for high performance tires.
In the conventional design of a tread for a pneumatic tire there are provided ground or road contacting elements in the form of ribs or blocks. The ribs or blocks are spaced by non-road contacting grooves. The grooves are channels or voids which allow water to be moved into them so that the ground contacting surfaces can maintain good traction. In the absence of grooves, the tread under wet conditions would lose ground contact, a thin layer or film of water would be between the tire and the road and a phenomena called hydroplaning would result. Under severe hydroplaning conditions the tire loses traction and control of the vehicle can be lost.
The design of a tire tread is a compromise. Under dry conditions the maximum amount of tread contacting the road is optimum. For example, the tire treads used at the Indianapolis 500 race are smooth and 100% of the tread while in the footprint of the tire contacts the road. In the event of rain the race stops.
As one is required to drive under less than ideal dry conditions a tread with 100% ground contact is not practical. The tread is therefore provided with groves to accommodate wet or snowy road conditions. In passenger tires, the ratio of areas of ground contacting elements to voids within the area of road contact, otherwise known in the tire art as the "footprint", is relatively high, generally in the 60% to 75% range. This high net-to-gross ratio enables the tire to be designed with minimal noise and vibration characteristics.
To design a tire with a high net-to-gross ratio yet good traction under wet conditions requires a tremendous amount of skill. The conflicting nature of the design requirements requires a fine balance in selecting the appropriate features for a successful tire tread design.
In high speed and high performance tires the performance of the vehicle is generally limited to the ability of the tires to respond.
This is particularly true in high speed cornering.
As a vehicle enters a turn the weight of the vehicle shifts, loading the outer set of tires while reducing the load on the inner set of tires. The tires deflect such that the outer shoulder area of the tread is in ground contact on the outer set of tires while the inner shoulder area of the lighter loaded inner set of tires is in ground contact. The resultant lateral loads must be absorbed by these ground contacting elements. It is desirable therefore that the ground contacting ribs or block elements be laterally stiff in order to absorb the lateral forces generated by the cornering vehicle.
The present invention describes a tread having improved lateral stiffness and superior high speed cornering.